1. Field
The invention relates to circuits for indicating that data has been deleted in a video frame storage track, and particularly to a circuit for generating a digital, data deleted, word corresponding to a selected deleted data display, which word is recorded in the storage track to indicate the track is available for recording.
2. Prior Art
Present video data storage systems for the most part utilize an analog format wherein the storage and retrieval of stored data is performed by continuously recording and storing the data in a magnetic disc, tape, etc., in short time segments, as in a disc stop/slow motion recorder/reproducer, in a cassette or a reel-to-reel recorder/reproducer, etc. The data location is identified by various edit markings made with pre-recorded cue tones, etc. It is becoming customary to control the recording, storing, interrogation or playback processes with computer means interfaced with the storage system. Ordinarily, tracks, blocks, or lengths of a disc, tape, etc., which contain data no longer required, are generally identified by the computer in a deleted data list stored in memory to provide an indication that the respective storage tracks, or blocks thereof, contain useless data and are available for subsequent recording of new data. Thus the data to be deleted is not erased when it is no longer required, but is instead obliterated with new data recorded over the useless data and stored at the identified location. In such systems, it is possible to interrogate the old data via computer and not know whether the data is up-to-date, useful, or deleted data.
Recent developments in the digital data storage area provide for the digital storage of television fields or frames, particularly as in circular tracks on rotating disc means. In such systems, it is highly desirable to provide some random access means for identifying any tracks in which the data is to be or has been deleted, such that upon interrogation thereof a readily visible, audible, or electronically detectable indication of the track availability is generated. A visual indication is particularly desired in a television signal storage system used for providing still displays so that the operator of such a system is able to readily distinguish between tracks containing useful data and tracks not containing useful data. While tracks containing television data no longer needed can be erased, if playback of such a track is requested, the display during such playback will be blank. Blank displays will also occur for some system malfunctions. Providing a visible indication on the display of a deleted track of data provides a convenient way of distinguishing a deleted track of data from a malfunction.